style: apply CSharpier formatting to all C# sources

Repo-wide sweep with the pinned CSharpier 1.3.0 tool. Whitespace and
line-wrapping only; OpenNest.Engine.Tests (109) and OpenNest.IO.Tests
pass after reformat, full solution builds 0 errors.

Added .csharpierignore so csproj/config XML keeps its existing layout
(CSharpier's XML wrapping churns attributes with zero benefit).

Formatting is now enforceable: dotnet csharpier check . passes.

OpenNest.Engine/Jobs/NestJobPart.cs

@@ -5,12 +5,18 @@ namespace OpenNest;
 /// <summary>An immutable requirement, independent of drawing names, UI state, and drawing quantity counters.</summary>
 public sealed class NestJobPart
 {
-    public NestJobPart(string id, PartGeometrySnapshot geometry, int quantity, int priority = 0,
-        RotationPolicy rotation = null)
+    public NestJobPart(
+        string id,
+        PartGeometrySnapshot geometry,
+        int quantity,
+        int priority = 0,
+        RotationPolicy rotation = null
+    )
     {
         ArgumentException.ThrowIfNullOrWhiteSpace(id);
         ArgumentNullException.ThrowIfNull(geometry);
-        if (quantity <= 0) throw new ArgumentOutOfRangeException(nameof(quantity));
+        if (quantity <= 0)
+            throw new ArgumentOutOfRangeException(nameof(quantity));
         Id = id;
         Geometry = geometry;
         Quantity = quantity;
@@ -20,6 +26,7 @@ public sealed class NestJobPart
 
     public string Id { get; }
     public PartGeometrySnapshot Geometry { get; }
+
     /// <summary>Positive number requested; never decremented by placement code.</summary>
     public int Quantity { get; }
     public int Priority { get; }